The present invention relates to an apparatus for and a method of evacuating a vacuum chamber (process chamber) of, for example, a semiconductor fabrication facility or the like.
FIG. 7 of the accompanying drawings shows an evacuating path for evacuating a vacuum chamber 10, which is used in an etching apparatus, a chemical vapor deposition apparatus (CVD), or the like for a semiconductor fabrication process. To the vacuum chamber 10, there is connected an inlet port 14a of a vacuum pump 14 of an evacuating system 12. The vacuum pump 14 has an outlet port 14b connected to a discharge pipe 16. The vacuum pump 14 increases the pressure of a process gas discharged from the vacuum chamber 10 to the atmospheric pressure. The vacuum pump 14 has conventionally been in the form of an oil rotary pump, but primarily comprises a dry pump at present.
If the vacuum level required by the vacuum chamber 10 is higher than the vacuum level that can be acquired by the vacuum pump 14, then an ultrahigh vacuum pump such as a turbo-molecular pump or the like may be positioned upstream of the vacuum pump. If the process gas is of a type that cannot be discharged directly into the atmosphere, then a discharge gas processing facility is connected to the discharge pipe 16.
Heretofore, it has generally been customary to use an induction motor rotatable at a rated rotational speed as a motor 20 of the vacuum pump 14 of the evacuating system 12. In order to allow a large amount of gas to evacuate smoothly when the pump is started or when the atmosphere air is introduced in the chamber, and also to keep the back pressure on the vacuum pump 14 in an allowable range, the discharge pipe 16 has had an inside diameter of about 40 mm if the process gas is discharged at a rate of about 2000 L/min, for example.
Usually, the vacuum chamber of the semiconductor fabrication facility is placed in a clean room, and hence the discharge pipe is occasionally laid over a long distance in the clean room up to the external space. If the discharge pipe is large in diameter, then it will take up a costly space and have its layout limited due to interference with outer component devices of the semiconductor fabrication facility. If the discharge pipe is small in diameter, then it cases an undue increase in the back pressure on the vacuum pump at the time a large amount of gas flows when the pump is started or the atmosphere air is introduced, with the result that the vacuum pump tends to fail to operate due to an excessive load. Therefore, there is a certain limitation to reducing the diameter of the discharge pipe.
The present invention has been made in view of the above drawbacks. It is an object of the present invention to provide an apparatus for and a method of evacuating a vacuum chamber with an evacuating system which includes a discharge pipe having a reduced diameter for space saving, and which operates stably by avoiding overloaded operation.
According to the present invention, an apparatus for evacuating a vacuum chamber through a discharge pipe with a vacuum pump having a variable rotational speed comprises a controller for controlling the rotational speed of the vacuum pump to keep a back pressure on the vacuum pump in a predetermined target range, and a discharge pipe connecting an outlet port of the vacuum pump to the atmospheric port and having a diameter corresponding to a specific flow capability, the diameter being less than a predetermined diameter corresponding to an evacuating flow capability of the vacuum pump.
According to the present invention, the apparatus further comprises a back pressure sensor connected to a discharge port of the vacuum pump, for; detecting a back pressure on the vacuum pump, wherein the controller controls the rotational speed of the vacuum pump based on a detected output from the back pressure sensor. Therefore, the back pressure can be controlled accurately at all times to operate the evacuating apparatus stably.
According to the present invention the controller controls the rotational speed of the vacuum pump to keep the detected output from the back pressure sensor in a predetermined target range.
According to the present invention the controller controls the rotational speed of the vacuum pump to prevent the detected output of the back pressure sensor from exceeding a predetermined target value.
According to the present invention the apparatus further comprises a booster pump connected to the discharge pipe in series with the vacuum pump, wherein the controller controls to start the booster pump when the detected output from the back pressure sensor results in insufficient evacuating capability for the vacuum pump. Therefore, the evacuating apparatus is thus capable of handling a large evacuating load while saving energy.
According to the present invention the controller controls the rotational speed of the vacuum pump according to a previously inputted pattern of changes in the rotational speed. The back pressure can thus be controlled with a simple apparatus arrangement, and the evacuating apparatus can start up stably.
According to the present invention the discharge pipe has a flow capability less than the evacuating capability of the vacuum pump. Therefore, the space required for piping is reduced, and the space in an expensive clean room can be effectively utilized. The pipe and the apparatus are easily joined to each other.
According to the present invention, there is provided a method of evacuating a vacuum chamber through a discharge pipe with a vacuum pump having a variable rotational speed, which comprises the steps of connecting a discharge pipe from an outlet port of the vacuum pump to the atmospheric port, the discharge pipe having a flow capability smaller than an evacuating flow capability of said vacuum pump, and detecting a back pressure on the vacuum pump and controlling the rotational speed of the vacuum pump based on the detected back pressure to keep the back pressure in a predetermined target range.
According to the present invention a booster pump is connected to the discharge pipe in series with the vacuum pump, and the method further comprises the step of starting the booster pump when the detected back pressure on the vacuum pump results in insufficient evacuating capability for the vacuum pump.
According to the present invention, the method further comprises the step of controlling the rotational speed of the vacuum pump according to a previously inputted pattern of changes in the rotational speed in an initial period of evacuating the vacuum pump.
According to the present invention, there is provided a method of evacuating a vacuum chamber through a discharge pipe with a vacuum pump having a variable rotational speed, which comprises the step of controlling the rotational speed of the vacuum pump according to a previously inputted pattern of changes in the rotational speed in an initial period of evacuating the vacuum pump.
According to the present invention, the rotational speed increases at a rate selected to keep an initial peak of the back pressure in evacuating the vacuum chamber, equal to or below a predetermined value.
According to the present invention, the rotational speed increases stepwise.